The CDMA technique is used in third generation systems such as the Universal Mobile Telecommunication System (UMTS).
As shown in FIG. 1, a mobile radio network generally includes a set of base stations and base station controllers. In the UMTS, this network is called the UMTS terrestrial radio access network (UTRAN), a base station is called a Node B, and a base station controller is called a radio network controller (RNC).
The UTRAN communicates both with mobile stations, which are called user equipments (UE), via a Uu interface, and with a core network (CN) via an Iu interface.
As shown in FIG. 1, the RNCs are connected:                to the Node B via an Iub interface,        to each other via an Iur interface, and        to the core network CN via an Iu interface.        
The RNC that controls a given Node B is called the controlling radio network controller (CRNC) and the CRNC is therefore connected to the Node B via the Iub interface. The CRNC has a load control function and a radio resource allocation control function for the Node B that it controls.
The RNC for a given call relating to a given user equipment UE is called the serving radio network controller (SRNC) and is connected to the core network CN via the Iu interface. The SRNC has a control function for the call concerned, including functions of adding or removing radio links (in accordance with the macrodiversity transmission technique) and monitoring parameters that may change during a call, such as bit rate, power, spreading factor, etc.
In CDMA systems radio interface capacity limitations are fundamentally different from those of systems using other multiple access techniques, such as the time division multiple access (TDMA) technique. The TDMA technique is used in second generation systems such as the Global System for Mobile communications (GSM). In CDMA systems, all users share the same frequency resource at all times. The capacity of these systems is therefore limited by interference, and for this reason these systems are known as soft limited systems.
This is why CDMA systems use algorithms, such as load control algorithms which prevent, detect and if appropriate correct overloads, in order to prevent quality being degraded, and call admission control algorithms which decide if the capacity of a cell not being used at a given time is sufficient to accept a new call in that cell (as a function of various parameters such as the service required for that call, etc.). In the following description these algorithms are referred to generically as load control algorithms.
These algorithms usually use only radio criteria and are usually implemented in the CRNC, which has no information about the processing capacity of each Node B that it controls. This being the case, it is possible for a new call to be accepted by the CRNC but in the end to be rejected for want of Node B processing resources, for example, which leads to unnecessary additional processing in the CRNC and additional exchanges of signaling between the CRNC and the Node B.
Of course, it would be possible to avoid these problems by providing the Node B with sufficient processing resources to cover all situations, including that of maximum capacity (corresponding to the case of a very low level of interference). But this would lead to costly base stations which would have more capacity than necessary most of the time. In addition, in the case of progressive introduction of the services offered by these systems, the processing capacity of the base stations may be limited when the systems begin to be put into service, and then progressively increased afterwards.
It would therefore be desirable for load control in this kind of system to allow for the base station (Node B) processing capacity.
FIGS. 2 and 3 respectively show the main sending and receiving processing operations used in a base station, such as a Node B in the UMTS, for example.
FIG. 2 shows a sender 1 including:                channel coder means 2,        spreader means 3, and        radio frequency transmitter means 4.        
The various processing operations are familiar to the person skilled in the art and do not need to be described in detail here.
Channel coding uses techniques such as error corrector coding and interleaving to protect against transmission errors. This is known in the art.
Coding (such as error corrector coding) introduces redundancy into the information sent. The coding rate is defined as the ratio of the number of information bits to be sent to the total number of bits sent or coded. Various levels of quality of service can be obtained using different types of error corrector code. For example, in the UMTS, a first type of error corrector code used for a first type of traffic (such as high bit rate data) is a turbo code and a second type of error corrector code used for a second type of traffic (such as voice or data at a lower bit rate) is a convolutional code.
Channel coding usually also includes bit rate adaptation to match the bit rate to be sent to the bit rate offered for sending it. Bit rate adaptation can include techniques such as repetition and/or puncturing, the bit rate adaptation rate being then defined as the repetition rate and/or puncturing rate.
The raw bit rate is defined as the bit rate actually passing over the radio interface. The net bit rate is the bit rate obtained after deducting from the raw bit rate everything that is not useful to the user, in particular redundant bits introduced by coding.
Spreading uses the well known principles of spectrum spreading. The length of the spreading code used is called the spreading factor.
In a system such as the UMTS in particular, the net bit rate (also referred to hereinafter simply as the “bit rate”) can vary during a call and the spreading factor can vary as a function of the bit rate to be sent.
FIG. 3 shows a receiver 5 including:                radio frequency receiver means 6, and        received data estimator means 7, including despreader means 8 and channel decoder means 9.        
The above processing operations are also familiar to the person skilled in the art and therefore do not need to be described in detail here.
FIG. 3 shows one example of the processing that can be carried out in the despreader means 8. Here the processing corresponds to that used in a Rake receiver to improve the quality of received data estimation by exploiting multipath phenomena, i.e. propagation of the same source signal along multiple paths, due in particular to multiple reflections from objects in the environment. In CDMA systems, unlike TDMA systems in particular, the multipath phenomenon can be used to improve the quality of received data estimation.
A Rake receiver includes a set of L fingers 101 to 10L and combiner means for combining signals from the various fingers. Each finger despreads the signal received over one of the various paths determined by estimator means 12 for estimating the impulse response of the transmission channel. The combiner means 11 combine the despread signals corresponding to the respective paths using a processing operation for optimizing the quality of received data estimation.
The technique of reception using a Rake receiver is also used in conjunction with the macrodiversity transmission technique, whereby the same source signal is sent simultaneously to the same mobile station by a plurality of base stations. The macrodiversity transmission technique not only improves reception performance, through using a Rake receiver, but also minimizes the risk of call loss in the event of a handover. For this reason it is also known as soft handover, as opposed to the hard handover technique whereby a mobile station is connected to only one base station at any given time.
The received data estimator means can also use various techniques for reducing interference, for example the multi-user detection technique.
A plurality of receive antennas can also be used. The received data estimator means then further include combiner means for combining signals obtained from the receive antennas, again in such a manner as to optimize the quality of received data estimation.
Channel decoding includes functions such as de-interleaving and error corrector decoding. Error corrector decoding is generally much more complex than error corrector coding, and can use techniques such as maximum likelihood decoding. A Viterbi algorithm can be used for convolutional codes, for example.
To be able to process several users simultaneously, a Node B includes a set of senders and receivers, such as the sender and the receiver referred to above. Thus a Node B requires a high processing capacity, in particular in the receiver, for received data estimation.
As previously indicated, it is therefore desirable if load control in a system such as the UMTS, for example, takes account of the base station processing capacity.
In the case of the UMTS, the document 3G TS 25.433 published by the 3GPP (3rd Generation Partnership Project) provides for the Node B to signal to the CRNC its overall processing capacity (called its capacity credit) and the amount of that capacity credit (called the cost) for each value of the spreading factor SF available in the system. The total cost for the available spreading factors is called the capacity consumption law. A Node B signals this information to the CRNC each time that the processing capacity of the Node B changes, by means of a “Resource Status Indication” message, or in response to a request from the CRNC, by means of an “Audit Response” message.
The CRNC then updates the remaining credit, on the basis of the consumption law, in particular, in the UMTS:                for the dedicated channels, during the radio link set-up, radio link addition, radio link deletion and radio link reconfiguration procedures defined in the document 3G TS 25.433 published by the 3GPP, and        for the common channels, during the common transport channel set-up, common transport channel deletion and common transport channel reconfiguration procedures defined in the document 3G TS 25.433 published by the 3GPP.        
The above procedures are called Node B Application Part (NBAP) procedures and the corresponding signaling messages are called NBAP messages.
Two different consumption laws are defined in the 3G TS 25.433 standard, one for the dedicated channels and one for the common channels. A dedicated channel is a channel assigned to a given user and a common channel is a channel shared between several users. For example, the UMTS includes a dedicated channel (DCH) and common channels including a random access channel (RACH), forward access channel (FACH), common packet channel (CPCH), downlink shared channel (DSCH), etc.
The applicant has noticed that the credit mechanism described in the current version of the 3G TS 25.433 standard still causes problems.
A first problem is that no account is taken of the specific nature of the DSCH.
Although the DSCH is in fact a common channel, it is always associated with a dedicated channel DCH, and set-up, deletion and reconfiguration procedures concerning the DSCH simultaneously concern the DCH. For example, for a radio link set-up operation, either one or two operations can be effected: one operation for the DCH and, if a DSCH is associated with the DCH, one operation for the DSCH.
Accordingly, even though the DSCH is a common channel, to simplify the capacity credit updating operations, it would be more logical for this channel to be taken into account in the consumption law for the dedicated channels.
However, the allocation cost for the dedicated channels is different according to whether the radio link concerned is a first radio link or not (the latter situation applies if the UE has more than one radio link in the same Node B, i.e. if the UE is in a soft handover situation with that Node B). Accordingly the 3G TS 25.433 standard specifies two costs that are taken into account for a first radio link, namely a Radio Link cost (RL cost) and a Radio Link Set cost (RLS cost); for an additional radio link, only the RL cost is taken into account.
The soft handover or softer handover technique is generally not used for the common channels, and in particular for the DSCH. The DSCH therefore gives rise to particular problems with applying the credit mechanism, which require a solution.